Making your own tack for your horses has a big upside. It's custom fit for the horse and the quality is as good as you can make it. I made the saddle for my pack horse and it's lasted for 12 years now and has seen all sorts of rough duty. Nothing has ever failed, and I don't ever expect it to. My saddle for my trail horse was made for me by a saddle maker I know since I don't have some of the equipment needed for the job. It too is custom fit and when you ride for days on end having a saddle that fits the horse and your backside well can be a blessing. This post is about how I made a pack saddle.
The first thing you need is a sewing machine that can accept heavy duty needles and thread and go through at least 4 layers of heavy weight duck canvas. I use duck canvas because it's relatively inexpensive, comes in a variety of neutral colors, and can be made water resistant or nearly water proof. A mixture of beeswax, and linseed oil makes for a good water resisting agent or you can use a silicone based commercial product.